The long-term goal of this project is to enhance our understanding of the signaling cross-talk between the phytohormones auxin and ABA. The recent cloning of IBR5, encoding a putative dual-specificity phosphatase and the subject of this proposal, revealed a novel point of interaction between auxin and ABA signal transduction. Several approaches will use IBR5 to gain greater understanding of the relationship between auxin and ABA. Firstly, suppressors if ibr5 auxin insensitivity and ABA insensitivity will be isolated (Aim 1). These suppressors will be phenotypically characterized (Aim 2) and the defective genes will be cloned (Aim 3). At least some of these suppressors are expected to carry lesions in IBR5 substrate genes. Both cloning of suppressors and co-immunoprecipitation will be used to identify potential IBR5 substrates (Aim 4). By studying and cloning suppresors, as well as identifying IBR5 substrates, a more in-depth understanding of auxin and ABA cross-talk will be gained.